In recent years, white light emitting devices using a gallium nitride (GaN) based light-emitting diode (LED) as semiconductor light emitting device and a phosphor as wavelength conversion material in combination have been attracting attention as light sources of image displays or lighting systems for their advantages such as low power consumption and long lasting quality. With this attention, development of a phosphor that is easy to manufacture, high in emission intensity, uniform in particle diameter, and further, capable of realizing a light emitting device with high color rendering has been desired.
Patent Document 1 discloses a candidate of such a phosphor that can meet the above-mentioned requirements. The phosphor, represented by the general formula (X) below, has its maximum emission peak of the emission spectrum within the wavelength range of from 485 nm to 555 nm and comprises a compound having a specific chemical composition as its host crystal. In the host crystal, trivalent cerium (Ce3+) is at least contained as activator element (luminescent center element). This phosphor is hereinafter abbreviated as “CSO phosphor”, as appropriate.M1aM2bM3cOd  (X)(In the formula (X), M1 represents an activator element including at least Ce, M2 represents a bivalent metal element, and M3 represents a trivalent metal element. a, b, c and d are numbers in the ranges of 0.0001≦a≦0.2, 0.8≦b≦1.2, 1.6≦c≦2.4 and 3.2≦d≦4.8, respectively.)    [Patent Document 1] Japanese Patent Laid-Open Publication (Kokai) No. 2006-45526